Alkali metal tetrahaloaluminates and, particularly, lithium aluminum chloride, are low melting salts which are known to be useful as electrolytes in non-aqueous power sources such as thermal batteries and primary or secondary cells, as low melting point solvents in spectroscopy, and in other applications for which low melting point salts are employed. While the potential value of such low melting salts in a variety of applications is substantial, their utility has been limited in the past in certain applications by the fact that such materials are normally obtained in relatively impure form from known production processes, whereas their use applications require a highly purified product. More specifically, lithium aluminum chloride and similar salts which have been prepared in the past normally contain substantial amounts of impurities, including oxygen-containing materials such as water and the hydroxides, inorganic metal salts, carbon derived from carbonaceous solvents or organic reactants, and metals such as iron, among others. For this reason, lithium aluminum chloride and other alkali metal tetrahaloaluminates are normally heavily discolored as manufactured, indicating a substantial content of the foregoing impurities.
Purification of lithium aluminum chloride and similar alkali metal tetrahaloaluminates is difficult since treatments suitable for the removal of one type of impurity seldom remove other impurities, and, indeed, make such removal more difficult in some cases. Moreover, inasmuch as aluminum chloride has a high vapor pressure at atmospheric pressure, it may vaporize from the lithium aluminum chloride, for example, if the material is heated during the purification treatment. When aluminum chloride is lost in this way, the lithium chloride or other alkali metal halides which remain are difficult to separate from the desired product.